Increased volumes of orbital and ventricular CSF may cause ocular changes in astronauts

Research presented at the annual meeting of the Radiological Society of North America (27 November–2 December 2016, Chicago, IL, USA) has revealed that visual impairment intracranial pressure, a problem affecting astronauts involved in prolonged space missions, may be caused by changes in CSF levels.

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In recent years, flight surgeons and scientists at NASA have noticed that many astronauts suffer from blurry vision; in addition to this, flattening occurs at the back of their eyeballs and inflammation of the head of their optic nerves has been observed, amongst other structural changes. This syndrome has been reported in nearly two-thirds of astronauts after long-duration missions aboard the International Space Station.

Noam Alperin (University of Miami, FL, USA), lead author of the study, explained the problem: “People initially didn’t know what to make of it, and by 2010 there was growing concern as it became apparent that some of the astronauts had severe structural changes that were not fully reversible upon return to Earth. If the ocular structural deformations are not identified early, astronauts could suffer irreversible damage. As the eye globe becomes more flattened, the astronauts become hyperopic, or far-sighted.”

It has previously been speculated that these visual and structural problems are caused by a shift of vascular fluid toward the upper body that takes place when astronauts spend time in the microgravity of space. However, due to the potential effects that microgravity may have on CSF, the researchers thought that changes in the levels of this fluid could be responsible for visual impairment intracranial pressure. Alperin explained: “On Earth, the CSF system is built to accommodate these pressure changes, but in space the system is confused by the lack of the posture-related pressure changes.”

In their work, Alperin and his team performed high-resolution orbit and brain MRI scans before and shortly after spaceflights for seven long-duration mission astronauts deployed at the International Space Station. They then compared these results with those from nine short-duration mission space shuttle astronauts. The investigators found that, compared to short-duration astronauts, long-duration astronauts had significantly increased post-flight flattening of their eyeballs and increased optic nerve protrusion. The long-duration astronauts also displayed significantly increased post-flight volumes of orbital and ventricular CSF.

Alperin concluded: “The research provides, for the first time, quantitative evidence obtained from short- and long-duration astronauts pointing to the primary and direct role of the CSF in the globe deformations seen in astronauts with visual impairment syndrome.” Now that the origin of space-induced ocular changes has been elucidated further, it will be important to develop countermeasures to protect astronauts from the effects of long-duration exposure to microgravity.